This invention relates generally to a bearing system for a launched projectile, and in at least one embodiment, relates to an internal bearing system for a spin-stabilized and/or a fin-stabilized projectile.
Spin-stabilized projectiles may include a guided portion which, after initially spinning upon launch, becomes relatively stationary compared to another portion of the projectile that continues to spin. The stationary portion may include aerodynamic surfaces which may be manipulated to assist in ultimately guiding the projectile towards a target. Similarly, fin-stabilized projectiles, which have both rear fins and forward canard fins, could use rear-mounted fins for guiding the projectile.
Lightweight, low-drag bearings may be desirable for use in such projectiles, as bearings used in spin-stabilized projectiles must survive excessively large loads, such as during the set-back, balloting, and set-forward phases during launch. Such an arrangement may be desirable for the nose and/or tail section in either a spin-stabilized or fin-stabilized projectile.
Also, it may be desirable to size the projectile's bearings more for in-flight loads than for launch loads, since such in-flight loads are typically much lower than launch loads.
Additionally, lighter-weight bearings may result in a lighter-weight projectile, which may in turn, aid in improved stability and on-target delivery and/or increased warhead carrying capability.
As used herein, “set-back” refers to the phenomenon of internal components within the body portion of the projectile tending to resist motion and shift rearwardly relative to the body portion as the projectile experiences forward motion upon being subjected to the acceleration forces from a launch. The term, “set-forward,” as used herein, refers to how the internal components within the body portion of the projectile, upon being released from the forces causing set-back, tend to rebound and move forward relative to the body portion and how such components may oscillate with respect to the body portion until general equilibrium is reached. The term, “balloting,” as used herein, refers to the motion induced to the projectile and its internal components as the projectile in essence bounces laterally back and forth, in contacting the interior of the barrel as it moves down the barrel during launch. Balloting also refers to the movement the projectile experiences as it is exposed to the forces of gases exiting the barrel around the projectile as it leaves the barrel. Balloting can occur during setback, before set-forward, and/or during set-forward. As used herein, “in-flight” loads or forces refers to aerodynamic loads experienced by the projectile in flight and also to imperfections and/or anomalies in the projectile which may tend to cause imbalance in the projectile as it spins.